Marth Tech: Shield SDI/ASDI
Description / How To Perform
Similar to regular 
SDI, you can affect your characters position during shieldstun with inputs on the analog stick. Unlike regular SDI Shield SDI is horizontal only, and you also must allow the analog stick to fully reset to neutral between each input.
There is also a Shield version of ASDI, but instead of holding the C-Stick in a direction to ASDI while in Hitstun, Shield-ASDI is done by holding the analog-stick in a direction to ASDI in that direction while in Shieldstun.
Difficulty: 
(Expert)
Usefulness: (Occasionally Useful)
Extra Info
Shield SDI/ASDI can sometimes be used to avoid shine-grab on your shield from Fox or Falco.
Shield SDI affects your position by roughly two thirds of what regular SDI does, and ASDI's effect is half of the respective versions for both.
In most situations using a Lightshield serves the same purpose as using Shield SDI/ASDI, but your shield would be significantly more damaged in the process.